Process of producing hydrated lime



Patented Jan. 4, 1927.

UNITED srarss WILLIAM a. season, or answer, VIRGINIA," I

rnoonss or rnonucme HYDRATED L ME;

No Drawing.

This invention relates to processes of producing hydrated lime; and itcomprises as a new article a dry hydrated lime existing as amass ofextremely fine particles, said lime having a plasticity in excess of 200and being substantially completely miscible with water to make milk oflime of the ordinary properties; and it further comprises a process ofslaking lime to produce dry hydrate having a plasticity in excess of 200wherein quicklime is ground to 100 mesh fineness or finer and the fineground lime is quickly admixed with a limited amount of water, admixturebeing completedprior to occurrence of any substantial hydration and theamount of water being such as to give a dry hydrate without a rise intemperature above, say, 105 0.; all as more fully hereinafter set forthand as claimed.

Dr hydrated limes vary extremely in plasticity and these variations areof great working importance. Commercially, those limes showing aplasticity less than 200 on Emleys plasticimeter (the usual instrumentfor testing described in the Technologic Pa er No. 169 of the Bureau ofStandards and further illustrated in the Book of Standards for 1925,published by the A. S. T. M. under standard specifications for hydratedlime for structural purposes) rank as fmasons hydrate, while thosehaving a plasticity over 200 are regarded as finishing hydrate.v Verymany attempts have been made to produce dry hydrates :by quick methodswhich on mixin with water will have the desirable plasticity andputty-like characteristics of.- lime slaked in a mortar box by a skilledWorkman, but without en-,

the success. The best ofthese products, such as those made from certainOhio limestones, will withstand the blotting paper test (described inthe technologic paper rezterred to above). These better grades can betroweled out on blotting paper to a con siderable extent; but most ofthe dry hydrates can be troweled out on/blotting paper only to a Llessextent. With the better grades, but little water is taken up by thepaper during the spreading; they owe their plasticity to the fact thatthey hold their water positively; in a condition that withstands thesuction of the paper.

None of the dry hydrates is completely miscible with water to formordinary milk of lime. lin this respect, they range from those whichwill give no milk of lime to Application filed April 4, 1924. Serial no.704mm but littlethese lattergrades referred to.

It is the object of thepresent invention to produce a newt-ype ofdryhydrate exist ing as a mass of extremely fine particles; such massbeing substantially completely miscible with Water to form limemilki ofthose which will give some,) althou h usually sing the better theordinary properties; and on mixingwith Water, giving'mortarsl of evenhigher grade than those produced by skilled work- I men in wet slaking.gThis lime will rank as a finishing hydrate since its plasticity-is over200. As a matter of 'fact its plasticity is ordinarily over 250. l 1

Slaking lump lime'or granular limeis a complex process taking placeinwst'ages, in point of time. Witha lump of lime of any size,penetration of thew'ater and reaction "are, so to speak, rhythmic. Thewater penetrates a short distance during what may be called a period ofincubation, before hydrar tion begins and further penetrationtemporarily ceases. With hydration comesa local rise in temperaturewhich may go. to a theoretical maximum of 580 (la-the equilibriumtemperature for calcium'hydrate. Rise in temperature to any such pointis, however, precluded by vaporization of water as it entersthe familiarsteaming. As. this; water vaporizes, there is a deposition of whateverlime it may carry with morefor less agglomeration of the hydrateparticles. Fresh water then penetrates beyond the point of hydration andthe action is repeated. While the actual amount ofheat liberated by theunion of water and lime "is a fixed quantity, and the consequent rise intemperature is also fixed, yet, because of this localization of action,in using ;a given amount of lime and of water, unduly high temperaturesare observed; that is, temperatures in excess of those which could becalculated fforthe total mass of lime and of'water. I

The described rhythmic actioninvolves, of course, a time factor and .itis-to some extent dependent upon the openness of the pores of-the lime;to the distance the water will penetrate during the period of incuba:tion and before its passageis interrupted by the hydrating action.During hydration in the described action, incoming water is removed byvaporization and. does not penetrate further. In any event, its passageis further impeded, temporarily; by the swelling of the lime particlesin hydration.

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together, without any localized, intermittent development of heat. Allparts of 'the lime being wet, and with the same amount of water, actionbecomes uniform. In one way of looking at it, I reduce the lime to sucha size that complete wetting can occur in a time well within the periodof incubation;

and surround each individual particle with just the amount of waterwhich will wet it,

will'hydrate it, and (by conversion into steam) will allow itstemperature to go to 100 C, but not much above. In so doing,

- although of course actually the same number will pass a 200 mesh. Insecuring this fine-' of heat units is liberated as in slaking coarserlime, yet the impression is that of a cooler slaking-there is nolocalized or temporary development of high temperatures. With a suitablefine grinding of quicklime and quick admixture of water, the whole massenters into quick interaction. And by properly roportioning the amountof water so as to rnish that needed for (a) hydration and (b) thatrequired for cooling by vaporization, the final resultis a mass of dryextremely fine-particled hydrate. As the entering water has had noopportunity to exercise any other function than that of hydration andof: vaporization, there is no solution or redeposition of the limeparticles formed in hydration- -they retain their initial extremely finestate of subdivision; the state of subdivision in which C210 is normallyleft on slaking lime. The part1- cles are in a colloid state and onaccess of water peptization takes place at once-milk of lime is formed.I q

The particular state of fineness required with any given lime dependssomewhat upon its character and is best determined by a speciallaboratory test hereinafter given. Ordinarily, however, I employ limewhich will pass at least a 100 mesh sieve (95 per cent through) and itis usually better so that it ness it is convenient to use working uponthe air flotation tprmciple 'lfhe uantity of water to be use is alwaysust .t at which will sufiice (a) for hydration and (b) for cooling byvaporization. Neither more nor less 15 wanted; although in calcu-.lating the amount required for cooling, due allowance mustbe made, ofcourse, for the heat capacity of the apparatus, radiation losses, etc.,so that the amount is usually somewhat less than pure theory wouldindicate.

The exact amount of water to be used also 105 C. and usually not above101 usually aeraeai depends upon the actual GaO present. The

gurpo'ses, as present, is

ideal amount of water for m regards the amount of actual a in the ratioof 1 part (3210 and 0.7%

parts H O at the ordinary temperature say, 20 C. Such a mixture initiallcontain 58 er cent CaO and 42per cent HZO. This is,-

owever, under, so to speak, adiabatic conditions where heat losses otherthan those due to volatilization of H O,'are not involved. Under idealconditions, this amount'of water will complete the slaking without arise in temperature over 100-105 C. and give a l21g 6irate of extremeplasticity; usually above With proper fine ground, high calcium lime andthe proper amount of water quickly I mixed, that is, with admixtureperfected during the period of incubation,,the mass I merely steams alittle and does .not go above Q. and 'ves a perfectly dry product ofextreme eness and plasticitz. Higher temperatures even up to 115 arepermissible but the stated limit of 100-105 C. is better. In theoperation just described, no opportunity is afforded for solution orrede osition of lime; and the fine particles prodaced in hydration donot increase in size or a glomerate. .The proportion of water whic ispresent for cooling purposes simply steams away, without opportunity forefi'ectmg solution or change 1n particle size,

In slaking, one gram molecule of CaO, or 56 grams with the theoreticalamount of water, one gram molecule or 18 grams,

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15,540 calories are evolved. To take care of u this evolved heat byvolatilization, leaving a dry lime hydrate at C., there is required, inaddition to the 18 grams of H 0, a further amount of water at, say, 20(1., amounting to about 23 grams. Taking volatilization water andhydration water together, there ,is obtained the theoretical-"'- ratioabove given, 1:0.724. But, as stated, because of working conditions,some subtraction from the amount of volatile water is practicable andnecessary; the subtraction corresponding to radiation, etc., losses bycooling in working.

The whole point of the invention is getting the lime fine enough so thata quick admix-- ture may be made with it, prior to hydration, of theexact amount of water required to hydrate and to cool (by vaporization)the mixture so that it shall take a temperature not over 105 C. andshall give a dry hydrate.

While in practice I alwa s grind the lime as fine as 100 mesh and of tengo above'200 mesh, these extreme finenesses are notalways necessary.With 'a porous, open-textured lime from particular imerocks or producedby-particular methods of. calcination, someai what coarser materials maysometimes be used. The exact fineness required for my urposes with angiven lime can be readily determined by w at ma be termed laboratoryduplication of p ant procedure. A sample-of fine ground lime is mixedwith the calculated amount of water in a roomy beaker shielded againstcooling. If the -'ent to afford complete hydration-there will 'beunslaked lime present. The quantity of water used in the beaker testisalways somewhat more than that required in actual plant practice; butthe difference is usually not great and is readil determined. In oneparticular plant wit a mixing time of one minute and theuse off anordinary pugmill system, for mixing, ordinaril I employ, instead of thestated ratio. 0 -1:0.72 about 1:0.50. In this articular case the wateradded instead of ing about 7 2 per cent of the lime is about per cent.

As stated, the best of the present dry hydrates withstand the blottertest in the sense that a pulped mass of such hydrated lime and water maybe troweled over a blotter; but they do not give up much water to theblotter-during spreading the piv l p with- 1th the stands the suction ofthe paper. present hydrate however, the pulped mass may be troweled overthe blotter and at the same time gives up considerable water to the atis, the present lime takes up enough more water In makin a plastic mass,because of its extremel co loid nature, to allow assage of some mto theblotter without orfeiting plasticity. This is a property which isextremely convenient in e water is peneoperation, because themason orplasterer desires some of the underlying layer to be wet in spreadingmortar. In this respect.

the present hydrate is much more advantageous than any of the priorpreparations dry or wet. There is also a difierence, an an advanta eous.one, in the consistence of the trowele mass-it has no graininess, but itis buttery or greasy in consistence.

WhatI claim is 1. The process of producing dry hydrated lime whiccomprises grinding quicklime to a fineness greater than 100 mesh andquickly admixing said ground lime with an amount of water suflicient toreact with all the lime to form a dry hydrate without a riseintemperature above 100-115 C. v

2. 1n the slaking of lime, the process which comprises grindingquicklime tosuch a fineness that intimate admixture with water can besecured prior to any substantial hydration and quickly adnnxing saidground lime with an amount of water suflicient to form a dry hydrate andto produce a ternerature between 100 and 115 C.

- 3. l the slaking of lime, the process which comprises grindingquicklime to such a fineness that intimate admixture with water can besecured prior to any substantial hydration and quickly admixing saidground lime with an amount of water suiiicient to form a dry hydrate andto produce a temperature not exceeding 115 C.

4. 1n the manufactureyof dry hydrated lime havin a plasticity in excessof 200, the process whlch comprisesgrinding quicklime to aboutlOO meshor finer and quickly mixing said ground lime with an amount of watersuflicient to form a dry hydrate and to produce a temperature notexceeding In testimony whereof, I have hereunto

